package com.dxh.sqlSession;

import com.dxh.config.BoundSql;
import com.dxh.pojo.Configuration;
import com.dxh.pojo.MappedStatement;
import com.dxh.utils.GenericTokenParser;
import com.dxh.utils.ParameterMapping;
import com.dxh.utils.ParameterMappingTokenHandler;

import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

/**
 * @author https://github.com/CoderXiaohui
 * @Description
 * @Date 2020-11-07 22:27
 */
public class SimpleExecutor implements Executor{
    /**
     *  就是在执行JDBC的代码
     */
    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        //1. 注册驱动，获取链接
        Connection connection = configuration.getDataSource().getConnection();
        //2. 获取SQL语句
        //假设获取的SQL是 : select * from user where id = #{id} and username = #{userName} JDBC是无法识别的，
        // 所以要转换sql ： select * from user where id = ？ and username = ? ，转换过程中还需要对#{}中的值进行解析存储
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);
        //3. 获取预处理对象：preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());
        //4. 设置参数
            //获取到参数的全路径
        String paramterType = mappedStatement.getParamterType();
        Class<?>  paramterTypeClass = getClassType(paramterType);
        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();
            //反射
            Field declaredField = paramterTypeClass.getDeclaredField(content);
            //暴力访问，防止它是私有的
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);
            //下标从1开始
            preparedStatement.setObject(i+1,o);
        }
        //5. 执行sql
        ResultSet resultSet = preparedStatement.executeQuery();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);

        ArrayList<Object> objects = new ArrayList<>();
        //6. 封装返回结果集
        while (resultSet.next()){
            Object o = resultTypeClass.newInstance();
            //元数据
            ResultSetMetaData metaData = resultSet.getMetaData();
            //metaData.getColumnCount() :查询结果的总列数
            for (int i = 1; i <= metaData.getColumnCount(); i++) {
                //字段名
                String columnName = metaData.getColumnName(i);
                //字段的值
                Object value = resultSet.getObject(columnName);
                //使用反射或者内省，根据数据库表和实体的对应关系，完成封装
                //PropertyDescriptor 内省库中的一个类，就是把resultTypeClass中的columnName属性来生产读写方法
                PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                Method writeMethod = propertyDescriptor.getWriteMethod();
                //把具体的值封装到o这个对象中
                writeMethod.invoke(o,value);
            }
            objects.add(o);
        }
        return (List<E>) objects;
    }

    @Override
    public Integer update(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
        //1. 注册驱动，获取链接
        Connection connection = configuration.getDataSource().getConnection();
        //2. 获取SQL语句
        //假设获取的SQL是 : select * from user where id = #{id} and username = #{userName} JDBC是无法识别的，
        // 所以要转换sql ： select * from user where id = ？ and username = ? ，转换过程中还需要对#{}中的值进行解析存储
        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);
        //3. 获取预处理对象：preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());
        //4. 设置参数
        //获取到参数的全路径
        String paramterType = mappedStatement.getParamterType();
        Class<?>  paramterTypeClass = getClassType(paramterType);
        List<ParameterMapping> parameterMappingList = boundSql.getParameterMappingList();
        for (int i = 0; i < parameterMappingList.size(); i++) {
            ParameterMapping parameterMapping = parameterMappingList.get(i);
            String content = parameterMapping.getContent();
            //反射
            Field declaredField = paramterTypeClass.getDeclaredField(content);
            //暴力访问，防止它是私有的
            declaredField.setAccessible(true);
            Object o = declaredField.get(params[0]);
            //下标从1开始
            preparedStatement.setObject(i+1,o);
        }
        int rowCount = preparedStatement.executeUpdate();
        return rowCount;
    }

    private Class<?> getClassType(String paramterType) throws ClassNotFoundException {
        if (paramterType!=null){
            Class<?> aClass = Class.forName(paramterType);
            return aClass;
        }
        return null;
    }

    /**
     * 完成对#{}解析工作：
     * 1. 将#{}使用?进行替换
     * 2. 解析出#{}里面的值进行存储
     * @param sql
     * @return
     */
    private BoundSql getBoundSql(String sql) {
        //标记处理类：配置标记解析器来完成对占位符的处理工作
        ParameterMappingTokenHandler parameterMappingTokenHandler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", parameterMappingTokenHandler);
        //返回解析后的sql
        String parseSql = genericTokenParser.parse(sql);
        //#{}里面解析出来的参数名称
        List<ParameterMapping> parameterMappings = parameterMappingTokenHandler.getParameterMappings();
        BoundSql boundSql = new BoundSql(parseSql,parameterMappings);
        return boundSql;
    }
}
